'Pressing the reset button" has become the favourite metaphor of the Obama administration's policy towards Russia. First pronounced by vice-president Joe Biden, then made flesh by secretary of state Hillary Clinton, when she handed a large red button to her Russian counterpart last month, it was mentioned again by the president during the Nato summit at the weekend.

Along Russia's north-western periphery, in countries with a long history of harsh treatment by the Kremlin, the metaphor is not being met with such enthusiasm. "When you press the reset button on your computer, you don't lose your memory files," Estonia's President Toomas Hendrik Ilves commented drily on the eve of the summit.

Opening a conference in Tallinn named after Lennart Meri, a former Estonian president who helped end the Soviet occupation and get the country into Nato, his quip was clearly meant as a warning to Obama. Most guests were advocates of a firm line with Russia, including many from Georgia, Ukraine, and the three Baltic states. Along with suspicion that the US president may be too eager to deal with Moscow, they were concerned that Nato's increasing focus on Afghanistan and other "out of area" crises is diverting the alliance from its core purpose.

To them it is a matter of geography and function. The Soviet Union has gone, but Nato's original rationale - the defence of its members against a military threat from Russia - remains unchanged. They also want to give new substance to the Nato treaty's Article 5, which recognises an attack on one member as an attack on all.

Several speakers even called for Nato to start drawing up detailed plans for deployment, resistance, and counter-attack in the case of a Russian intervention in central Europe or the Baltics. Last August's war in Georgia was cited as a precedent. During the cold war, they argued, Nato not only had contingency plans but openly conducted military exercises to test its readiness to repel a Soviet or Warsaw Pact advance. That practice should be revived so as to show Moscow that Nato's security guarantee for its new eastern members is not just a paper promise.

If put into action, their line would be seen by the Kremlin as a major provocation. No wonder Nato failed to come up with its much-promised new "security concept" last weekend. Instead, it has tasked a team of experts to find a compromise between the alliance's globalisers and those who maintain that Nato's priority is still a potential threat from Russia.

Obama is firmly with the former group. Indeed, his performance last week, at his first meeting with Russia's president Dmitry Medvedev in London and at the Nato summit, has confirmed a major shift in US attitudes. Historically, the ideological hawks on Russia were the Democrats. They were the ones who founded Nato in 1949, and after a swing back to quiet Republican accommodation under Eisenhower, it was Jack Kennedy who summoned the west to a crusade against communism. The US, he promised, was ready to pay any price, bear any burden, and meet any hardship in the common struggle.

But with the Republicans back in the White House, Nixon allowed his national security adviser, Henry Kissinger, a historian of 19th-century realpolitik, to launch an era of detente with Russia that produced a series of treaties to limit each side's nuclear arsenals. The zigzag pattern continued under Carter, Reagan, and Clinton, and was only broken by Bush, perhaps the most ferocious foreign policy ideologue ever to have occupied the White House. He tore up the anti-ballistic missile treaty and expanded Nato into the Baltics.

By contrast, Obama is back to Republican-style realism. He came to Europe last week with a laundry list of issues for agreement with the Russians, ranging from arms control to Iran, Afghanistan, and counter-terrorism. It was sensible pragmatic stuff, devoid of any lecturing. It is true that Nato's long communique repeated a ritual promise of eventual membership for Georgia and Ukraine as well as other items which irritate the Kremlin, but the other summit document, a more solemn Declaration of Alliance Security, made no reference to Russian "aggression" in the Caucasus or to Georgia and Ukraine by name at all.

In his own speeches and press conferences in Europe, Obama's only reference to potential new Nato members was couched in language that should satisfy Moscow. They would have to be states, he said, that "can contribute to common security and stability". Georgia, under its current leadership, is clearly not one of those, and even if a more democratic government were elected there, a country involved in a frozen conflict over divided territory cannot be described as stable. Obama, in short, has accepted the view of last August's events that most EU and Nato members take. They may not say it in public, but they think Georgia started an unnecessary war and Russia was bound to retaliate.

Amid all the possible challenges, Obama's European trip has helped show what issues he intends to be the foreign policy priorities of his presidency. His cards are on the table, and both leads are risky. One is a huge political investment in success in Afghanistan. The other, as gratifying as it was unexpected, is a massive push towards nuclear disarmament. The contrast with Bush is stark.

Moscow will be pleased. Desperate to be seen as a global player in spite of its economic weakness, the Kremlin has a dog in both fights. In Afghanistan, the Kremlin has a win-win hand. It will not send troops there and so will not be humiliated if Nato loses. If Nato succeeds against all the odds, Moscow's security will be enhanced. Meanwhile, the Russians can use their control of Central Asia to give or withhold US access to Afghanistan.

On nuclear arms control the Russians are major actors. They will have to be involved at every stage, whether it is safeguarding "loose nukes", preventing proliferation, or curbing arsenals. This gives them bargaining room.

The fact that Obama knows this but does not mind is a welcome sign of his seriousness. It is not just Russian leaders who must be relaxing. The world as a whole can breathe more easily, even if in the Baltics, where jagged slabs of sea-ice are still drifting in this year's uncertain spring, anxiety is still the dominant mood among the region's elites.j.steele@theguardian.com